The present invention relates to a directional exhaust valve for switchable onward flow of exhaust gas.
The following discussion of related art is provided to assist the reader in understanding the advantages of the invention, and is not to be construed as an admission that this related art is prior art to this invention.
Throughflow of an exhaust gas within an exhaust system is normally controlled by flaps. This type of control is realized by a rotary or translational movement of an individual flap so that the opening cross section of the respective pipeline is influenced. Junctions within the exhaust system are used as bypass to disperse inflowing exhaust flow to at least two continuing pipelines or to conduct the exhaust flow to only one of the pipelines.
Temperatures along the exhaust system can greatly vary in dependence on the distance to the combustion chamber. This directly impacts the construction of required control elements which have to be configured to withstand stress in general and changing thermal stress.
In particular when exhaust gas recirculation (EGR) in motor vehicles is involved for nitrogen oxide reduction, the control elements should be arranged as close to the region of the combustion engine as possible. The control elements configured as bypass are hereby exposed to temperatures of up to 950° C. Besides the thermal stress, tightness and smoothness as well as acoustics and service life place further constraints on the design of control elements. Control elements used in exhaust systems require greater adjustment and holding forces in order to realize the movement when switching the exhaust flow, whereas lesser forces are needed in the EGR region because of the significantly smaller mass flow rate while tightness is a primary consideration.
There are various ways to construct control elements. Simple throttles are mounted for example on a rotary shaft which extends through the pipe cross section. Their use in the EGR-region is however unsuitable because of the stringent requirement for tightness. Other examples include valve flaps that move translatorily or rotary valves. Control elements including the accommodated flaps are operated using electric, pneumatic or hydraulic drives. Such a bypass is realized within the exhaust system by directional exhaust valves to control at least three pipelines converging at a junction. A problem encountered in this context is the realization of a force balance with respect to the axis of employed flaps.
It would be desirable and advantageous to provide an improved directional exhaust valve to obviate prior art shortcomings and to enable smooth operation while yet providing superior tightness and accompanying acoustics.